1. Field of the Invention
The invention relates to a cetane number detection device and a cetane number detection method of detecting the cetane number of a fuel in an internal combustion engine, for example, a diesel engine or the like.
2. Description of the Related Art
The fuels used for operation of internal combustion engines vary in ignition quality depending on their cetane numbers. Therefore, technologies related to measurement methods for cetane number, control methods for the amount of fuel injection or the fuel injection timing according to the cetane number, etc. have been proposed.
For example, Japanese Patent Application Publication No. 2006-226188 (JP-A-2006-226188) describes a device that, at every time of start of the engine, determines the presence/absence of refueling and detects the cetane number from a correlation between the rate of heat generation from the combustion of an amount of fuel supplied by pilot injection and the cetane number. Japanese Patent Application Publication No. 2006-16994 (JP-A-2006-16994) describes a device that detects the cetane number from the ignition delay time at the time of a specific operation state. Japanese Patent Application Publication No. 2002-201997 (JP-A-2002-201997) describes a device that determines the cetane number from the coolant temperature at the time of start of the engine and the amount of time it takes to start the engine. Japanese Patent No. 2744507 describes a device that determines whether or not the present fuel is a low-cetane number fuel from an engine rotation speed fluctuation or an engine start rising time. Japanese Patent Application Publication No. 2006-188992 (JP-A-2006-188992) describes a device that detects refueling, and inputs information about the fuel into control means, and then controls the engine.
By the way, when an internal combustion engine is in a fuel-cut state, it is a common practice to execute a fuel injection into a combustion chamber for the purpose of measuring the cetane number, and to detect the cetane number of the fuel on the basis of the ignition timing at which the fuel is ignited. In this method, however, since the measurement of the cetane number cannot be performed until the vehicle decelerates, there is possibility of failing to start the internal combustion engine, for example, if a fuel of low cetane number has been supplied during the present stop of the vehicle.